Since a drive shaft spins at full engine t-pm in high gear, it must be straight and perfectly balanced (weight evenly distributed around center line of shaft). If NOT balanced, the shaft can vibrate violently. To prevent this vibration, drive shaft balancing weights are welded to the shaft at the factory. Small metal weights are attached to the light side to counteract the heavy side for smooth operation.

The drive shaft can be either open or enclosed, depending on the type of drive used. The HOTCHKISS drive has an open drive shaft that operates a rear axle assembly mounted on springs (fig. 5-2). The HOTCHKISS drive requires that the springs be rigid enough to withstand the twisting action (torque) of the rear axle and the driving and braking forces that the springs transmit to the frame. This type of drive is common to the equipment you will encounter in the Navy.

Another type of drive is a torque tube. Torque tubes differ from the Hotchkiss design in that a solid drive shaft is enclosed in a hollow torque tube and rotates within a support bearing to prevent whipping. One universal joint is used at the front of the drive

Figure 5-2.- Hotchkiss drive.

shaft, and the rear of the drive shaft is attached to the axle drive pinion through a flexible coupler.